As auto analyzers that analyze component amounts contained in a sample, devices that irradiate a sample, or a reaction solution in which a sample and a reagent are mixed, with light from a light source, measure the amount of transmitted light with respect to a single wavelength or a plurality of wavelengths obtained as a result to calculate the absorbance, and determine component amounts based on the relationship between absorbance and density in accordance with the Lambert-Beer law are used widely (e.g., Patent Literature 1). In such devices, numerous cells holding a reaction solution are arranged along the circumference of a cell disk that alternates between rotating and being stationary, and, while the cell disk is rotating, a data series of changes in the amount of light at given points in time (reaction process data) is measured as changes in the amount of received light over time for approximately ten minutes at regular time intervals by a transmitted light measuring unit disposed at a predetermined position.
Auto analyzers measure, as reactions of reaction solutions, two broad categories of reactions, namely color reactions between a substrate and an enzyme, and agglutination reactions between an antigen and an antibody. The former relate to biochemical assays which may be used to test for LDH (lactate dehydrogenase), ALP (alkaline phosphatase), AST (aspartate oxoglutarate aminotransferase), etc. The latter relate to immunoassays which may be used to test for CRP (C-reactive protein), IgG (immunoglobulin G), RF (rheumatoid factor), etc. Some substances measured by the latter immunoassays are found in blood in low concentrations, and thus require high sensitivity. For such substances, a reagent in which the surfaces of latex particles are sensitized (bound) with antibodies is used, and, as a component contained in the sample is recognized and agglutination is caused, the reaction solution is irradiated with light to measure the amount of light transmitted without being scattered by the latex clumps, thereby determining the amount of the component contained in the sample.
With respect to the above, there have been attempts to enhance sensitivity by measuring the amount of scattering light, instead of measuring the amount of transmitted light as is done in ordinary analyses. By way of example, there have been disclosed: a system in which transmitted light and scattering light are separated using a diaphragm, and absorbance and scattering light are simultaneously measured (Patent Literature 2); a feature whereby precision on the high-concentration side is enhanced by measuring reflected scattering light caused by large clumps that are formed as an agglutination reaction progresses (Patent Literature 3); a method in which integrating spheres are placed in front of and behind a reaction container, the respective average light amounts of forward scattering light and back scattering light are measured, and changes in turbidity caused by cell misalignment are corrected (Patent Literature 4); a method that provides for easier device size reduction and device adjustment by disposing a fluorescence/scattering light measurement detection system in the same plane as the cell rotation direction (Patent Literature 5); a turbidity measuring method in which turbidity is calculated based on the ratio between scattering light intensity and transmitted light intensity with respect to particles flowing in a flow cell (Patent Literature 6); etc.